1. Field of the Invention
The present invention pertains to a reciprocating multi-cylinder piston pump of the type generally used for oil field mud and injection fluid pumping and which is of a fabricated substantially all welded construction of both the fluid end section and the power end section.
2. Background Art
There are many applications for reciprocating piston pumps which are particularly adapted for pumping relatively large volumes of fluid at pressures of 3,000 to 5,000 psig. One of the more demanding applications for this type of pump is in oil field rotary drilling mud circulation service and for pumping fluids used in processes for enhanced recovery of subterranean petroleum deposits. The historic cyclical demand for oil field drilling mud pumps, for example, has made the capital investment necessary for producing these types of pumps generally unattractive to many machinery manufacturers. Oil field mud pumps have traditionally been designed as duplex reciprocating types having a double acting piston and cylinder arrangement which dictates the utilization of a crosshead mechanism for interconnecting the piston rod with a crankshaft and connecting rod or eccentric assembly. This general design concept has resulted in the development of relatively large frames or crankcase housings for the crank or eccentric shaft and crosshead mechanism, which housings have traditionally been formed as large unitary iron or steel castings. By the same token, the fluid end or cylinder assemblies together with the cylinder heads and valve housings have also been formed as relatively large castings or fabricated from steel billets which have been machined to form the necessary cylinder bores and connecting fluid passageways. Prior art methods of manufacturing large reciprocating piston type pumps using cast crankcases or power ends as well as cast fluid end or cylinder assemblies have required sizable investments in machine tools necessary to form the bearing bores and the crosshead guide bores. Moreover, the capital investment required to manufacture casting patterns and provide the available foundry facilities has also contributed to the high cost of oil field type reciprocating pumps.
Notwithstanding the problems associated with the cost of capital equipment necessary for fabricating oil well drilling mud pumps and the like, the nature of the application of this type of pump also requires that the pump be moved frequently from one drilling site to another. It is therefore also desirable to provide a pump which is as lightweight as possible and at the same time is able to withstand the mechanical stresses endured in pumping relatively large volumes of drilling mud at high working pressures. For example, a typical prior art drilling mud pump, capable of delivering from 200 gallons per minute to 600 gallons per minute at 1,000 to 3,000 psig, respectively, may weigh up to 52,000 lbs. complete with a standard supporting frame or skid. A pump of the aforementioned capacity typically has input power requirements ranging from 700 to 800 hp.
Accordingly, there has been a longfelt need for the development of a suitable reciprocating pump which is relatively lightweight while yet capable of reliable service under the operating specifications such as those indicated hereinabove and which may be fabricated without the tooling and other capital equipment requirements associated with the manufacture of large machines.
There have been several efforts in the prior art of reciprocating pumps to develop pumps of fabricated construction such as the manufacture of the crankcase using built up construction of welded together or mechanically fastened together plate and other structural parts. However, prior art efforts have primarily been directed to pump structures which merely use fabricated parts instead of cast parts, and the assembled power end frames and fluid ends still require extensive machining operations with large boring equipment. In fact, the configuration of some prior art fabricated pump structures actually increases the weight of the pump versus the weight of a comparable pump using cast crankcase or power end housings as well as cast cylinder assemblies. The problems associated with the need to provide accurate alignment of the bearings and bearing supports for the pump drive mechanism, including the jackshaft, the crank or eccentric shaft and the crosshead guides, have not been overcome with prior art designs. However, several problems associated with efforts to design a suitable completely fabricated reciprocating piston pump have been overcome with the present invention as will be appreciated by those skilled in the art.